The present invention relates to a sensor for detecting leaks of a corrosive liquid.
When a corrosive liquid such as hydrochloric acid leaks from a storage tank in an industrial plant or the like, extensive environmental pollution may occur. It is therefore essential for such leakage to be detected at an early stage. To meet this need, a corrosive liquid sensor as shown in FIGS. 3(A) and (B) has been proposed previously. FIG. 3(A) is a schematic cross-sectional view of the sensor, showing it in an exploded manner. FIG. 3(B) is a fragmentary top plan view of the sensor. This sensor includes a pair of insulating films 1a and 1b and a pair of metal wires, i.e., electrodes 2a and 2b. The insulating films 1a and 1b are formed from an insulating material such as Teflon.RTM. polytetrafluoroethylene which is not corroded by the corrosive liquid to be detected. The electrodes 2a and 2b are made of a metal such as aluminum which will be corroded by the corrosive liquid, and have a circular cross-section. The electrodes 2a and 2b are disposed between the insulating films 1a and 1b parallel to each other, and the insulating films 1a and 1b are placed on top of one another with the electrodes placed therebetween and are bonded together to form the sensor. In FIG. 3(A), these components are shown in an exploded manner, as described above, for convenience of illustration. As seen from FIG. 3(B), one of the insulating films 1a is provided with a large number of through-holes 4a and 4b which are aligned in two rows 3a and 3b extending along the electrodes 2a and 2b and are spaced apart from one another at predetermined intervals along each row, such that the electrodes 2a and 2b are exposed through these through-holes.
To detect the leakage of a corrosive liquid, this sensor is placed at a site where leakage may be expected, and the electrodes 2a and 2b which respectively act as electrodes are connected to a detecting circuit (not shown). If leakage occurs, the corrosive liquid which has leaked passes through at least a part of the through-holes 4a and 4b and enters the inside of the sensor. The detecting circuit is opened when at least one of the electrodes 2a and 2b are dissolved, thereby detecting the leakage of the corrosive liquid.
In this type of sensor, the metal wires 2a and 2b which serve as the electrodes generally have a diameter as small as about 0.6 mm, i.e., they present a small surface area to be melted by the corrosive liquid. Therefore, it takes a relatively long time for the electrode to be dissolved. In addition, even if the electrode is fused, both electrodes may be shorted due to the presence of the corrosive liquid. Because the natural resistance of the corrosive liquid is low, the circuit may not be completely opened, making accurate detection of the leakage difficult. FIG. 4 shows how the resistance detected in the above-described detecting circuit changes as the time passes when samples 1 and 2, which are provided by suitably dividing the sensor of FIGS. 3(A) and (B) into two halves longitudinally, are soaked in about 100 cc of hydrochloric acid having a concentration of 36 weight percent. As seen from the figure, the resistance, which was 10 ohms before the samples were immersed, only become about 70 ohms after 100 minutes of immersion. It is therefore clear that it is difficult for the sensor shown in FIGS. 3(A) and (B) to quickly and accurately detect leakages.
Accordingly, an object of the present invention is to provide a sensor for detecting leaks of a corrosive liquid which can solve the problems of the prior art by quickly and accurately detecting leakages of a corrosive liquid.